Atmospheric pollution is a phenomenon which gains in importance, as regards the sources of emission of the polluting compounds emitted as well as the impact of the pollution on man and on the environment. Carbon dioxide (CO2) is one of the greenhouse effect gases widely produced by man's various activities, notably by the combustion of fossil energies such as coal, natural gas and petroleum derivatives.
In order to reduce the amounts of greenhouse effect gases discharged to the atmosphere, it is possible to capture the carbon dioxide contained in industrial fumes, which are large stationary sources.
The composition of a fume corresponds, by volume, to about 75% nitrogen (N2), 15% carbon dioxide (CO2), 5% oxygen (O2) and 5% water (H2O). Various impurities such as sulfur oxides (SOx), nitrogen oxides (NOx), argon (Ar) and other particles are also present, in lower proportions, generally representing less than 2% by volume of the fumes. Typically, the composition in percent by volume of the fumes obtained by combustion of a natural gas can be: 2.5% O2, 71.6% N2, 0.6% Ar, 8.5% CO2, 16.3% H2O, 0.2% CO, and unburned compounds. Typically, the composition in percent by volume of the fumes obtained by combustion of coke can be: 5.7% O2, 75.2% N2, 1.0% Ar, 13.3% CO2, 4.8% H2O. These fumes are generally discharged to the atmosphere at a temperature ranging between 50° C. and 180° C., and at a pressure generally below 2 MPa.
In general, decarbonation and deacidizing of the fumes are carried out by washing the fumes with a solvent.
In order to remove 90% of the carbon dioxide contained in the fume, a solvent combining a great physical affinity or a great chemical affinity with the carbon dioxide to be absorbed is often used. Using a solvent consisting of water, alkanolamine or amine or of another basic compound, and an organic compound such as an alcohol, sulfolane or any other organic molecule with a high polar character allows to combine a high absorption capacity and a great chemical affinity between the solvent and the acid gases to be eliminated.
For example, a decarbonation method using washing with a solvent is described in the document entitled “Research Results for CO2 Capture from Flue Gas by Aqueous Absorption/Stripping”, by Rochelle, G. T.; Goff, G. S.; Cullimane, J. T.; Freguia, S.; presented at the Laurance Reid Gas Conditioning Conference, Feb. 25-27, 2002. Absorption of the carbon dioxide is achieved at temperatures ranging between 40° C. and 80° C.
These methods are however penalized by the solvent losses due to the solvent saturation of the fumes treated and to the solvent being mechanically carried along in the fumes. These losses are all the higher since the solvent constituents have a high vapour pressure.